Well treatment method employing new and improved drilling fluids and additives therefor

ABSTRACT

A process and composition are provided for permeability reduction in a hydrocarbon-bearing formation to improve hydrocarbon recovery therefrom. A moderately epichlorohydrin cross-linked, non-hydroxylpropylated starch is derived from high amylopectin waxy maize starch for use in drilling, workover and completion fluids. The starch is combined with xanthan gum and used in solutions of fresh water, non-saturated brine or saturated brine containing sized salt particles, typically sodium chloride, of various sizes, or sized calcium carbonate, or a combination of sized salt and sized calcium carbonate.

RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationSerial No. 60/080,484 filed Apr. 2, 1998, and is a division of U.S.patent application Ser. No. 09/282,896 filed Mar. 31, 1999, now U.S.Pat. No. 6,133,203.

TECHNICAL FIELD OF THE INVENTION

The invention relates, generally, to fluids used for drilling,completion and workover of oil, gas and geothermal wells in earthformations, and to additives for use in such fluids. More particularly,the invention relates to a new and improved starch which can be used toimprove various qualities of such fluids, for example, to controlfiltrate losses.

BACKGROUND OF THE INVENTION

It is well known in the art involving fluids used in the drilling,completion and workover of wells in earth formations, to include eithera fresh water solution, or a non-saturated brine solution, or asaturated brine solution, polymers, starches and bridging solids, forexample, as discussed in the SPE Paper No. 35332, entitled “Design andApplication of Brine-based Drilling Fluids”, authored by R. Swarthoutand R. Pearcy, presented at the International Petroleum Conference andExhibition in Mexico, in Villahermosa, Mexico, Mar. 5-7, 1996. Thecompletion of workover fluids using similar formulations are alsodiscussed in U.S. Pat. Nos. 4,822,500; 4,175,042; 4,186,803 and4,369,843.

U.S. Pat. No. 4,822,500 makes use of starch which is considered to be anepichlorohydrin crosslinked, hydroxypropyl starch manufactured from alow amylopectin maize starting material. This patent also discloses thecombination of xanthan gum with the low amylopectin starch, as well asparticle solids such as sized sale, for example, sized sodium chloride,in formulating well treating fluids.

Moreover, British Patent No. 2,086,923 assigned to Baroid Technology,Inc., the assignee of this present application, discloses thecombination of various polysaccharide gums, such as xanthan gum, withvarious starch derivatives. On page 3 of the British Patent No.2,086,923, for example, there is teaching that exemplary starchderivatives are the carboxyalkyl starch ethers such as carboxymethylstarch and carboxyethyl starch; hydroxyalkyl starch esters, such ashydroexethyl starch and hydroxypropyl starch; and mixed starch etherssuch as: carboxylalkyl hydroxyalkyl starch, e.g., methyl hydroxyethylstarch; alkyl carboxyalkyl starch, e.g., ethyl carboxymethyl starch.Exemplary polysaccharide gums include: the bipolymers such asxanthomonas (xanthan) gum; galactomannan gums, such as guar gum, locustbean gum, tara gum; glucomannan gums; and derivatives thereof,particularly the hydroxyalkyl derivates. For other exemplarypolysaccharide gums see U.S. Pat. Nos. 4,021,355 and 4,105,461.Especially preferred hydrophilic polymers are xanthan gum (XC polymer),carboxymethyl cellulose and hydroxyethel starch.

Various other starches can also be used in formulating drilling,completion and workover fluids, as is well known in this art, forexample, as discussed in Composition and Properties of Oil Well DrillingFluids, Fourth Edition, published by Gulf Publishing Co., Houston, Tex.,1980, authored by George R. Gray, H. C. H. Darley and Walter F. Rogers,at its pages 548-552. The use of xanthan gum in such fluids is alsodiscussed in the same reference, pages 554-556.

SUMMARY OF THE INVENTION

The invention comprises, generally, a new and improvednon-hydroxypropyl, epichlorohydrin crosslinked, high amylopectin, waxymaize starch having special utility as an additive for the drilling,completion and workover fluids used in oil, gas and geothermal wells.

As another feature of the invention, the non-hydroxypropyl,epichlorohydrin cross-linked, high amylopectin, waxy maize starch iscombined with xanthan gum with the combination having special utility asan additive for drilling, completion and workover fluids used in oil,gas and geothermal wells.

DETAILED DESCRIPTION OF THE INVENTION

The process of the present invention comprises preparing fluids fordrilling, completion and workover of well bores, drilling the borehole,circulating such fluids during the drilling of the borehole, andcompleting the preparation of the well bore.

Amylopectin is the term used to describe the outer, almost insolubleportion of starch granules. Amylopectin is a hexosan, a polymer ofglucose, and is a branched molecule of many glucose units, with amolecular weight distribution of 40,000 to 100,000. Amylose, on theother hand, is the inner, relatively soluble portion of starch granules,and is a hexosan, a polymer of glucose, and consists of long straightchains of glucose units, with a molecular weight ranging from 10,000 to100,000, joined by a 1,4-glycosidic linkage. Generically, the starchesused in the present invention are manufactured using maize as thestarting material. So-called regular maize (corn) contains approximately74% amylopectin and 26% amylose. Waxy maize is almost totallyamylopectin, being about 99% amylopectin or even 100% amylopectin, withonly traces, if any, of amylose. Amylopectin is more stable in saturatedsalt environments because of its branched-chain structure.

On information and belief, the epichlorohydrin cross-linked,hydroxypropyl starch discussed in U.S. Pat. No. 4,822,500 is formulatedfrom regular maize (low amylopectin, e.g., 74% amylopectin). In sharpcontrast, the starch according to the present invention is formulatedfrom a high amylopectin, usually 99% or greater, waxy maize starch toprovide a drilling fluid additive having improved filtration controlcharacteristics.

The starch derivative according to the present invention, when combinedwith xanthan gum in either a fresh water solution, or a non-saturatedbrine, or a saturated saline solution containing water soluble, sizedsalt particles, sized calcium carbonate particles, or combinationsthereof, decreases fluid loss in the well being treated and improves thesuspension characteristics thereof, decreases fluid loss in the wellbeing treated and improves the suspension characteristics of the wellfluid, whether in the drilling, completion or workover of the particularwell.

Starch is a natural polymer containing an abundance of hydroxyl groups.Each androglucose unit contains two secondary hydroxyls and a largemajority contain primary hydroxyls. These hydroxyls potentially are ableto react with any chemical capable of reacting with alcoholic hydroxyls.This would include a wide range of compounds such as acid anhydrides,organic chloro compounds, aldehydes, epoxy, ethylenic compounds, etc.When the specific chemical contains two or more molecules capable ofreacting with hydroxyl groups, there is the possibility of reacting twodifferent hydroxyls resulting in cross-linking between hydroxyls on thesame molecule or on different molecules.

The reaction conditions used in making cross-linked starches vary widelydepending upon the specific bi- or polyfunctional reagent used for thecross-linking. In general, most of the reactions are run in aqueoussuspensions of starch at temperatures ranging from room temperature upto about 50° C. Often an alkali such as sodium hydroxide is used topromote the reaction. The reactions are normally run under neutral tofairly alkaline conditions, but below the level which will peptize orswell the starch. If the cross-linking reaction is run in an aqueoussuspension of starch, when the desired level of cross-linking (usuallyas measured by some type of viscosity or rheology test) is reached, thestarch suspension is neutralized and the starch is filtered and washedwith water to remove salts, any unreacted reagent, and other impuritiesproduced by side reactions of the cross-linking reagent with water.Konigsberg U.S. Pat. No. 2,500,950 discloses the cross-linking of starchwith epoxyhalogen compounds such as epichlorohydrin.

The chemistry of starch and the preparation of a multitude ofderivatives thereof is well known. A book entitled “Modified Starches:Properties and Uses”,by O. B. Wurzburg, 1986 (CRC Press, Inc.; BocaRaton, Fla., U.S.A.) is an excellent source for information in thepreparation of starch derivatives.

The starch described in U.S. Pat. No. 4,822,500 is marketed by TexasUnited Chemical Corporation of Houston, Tex., under their tradenameFL-7. The starch is an epichlorohydrin cross-linked, hydroxypropylstarch formulated from a low amylopectin maize starch. The starchexhibits a high degree of epichlorohydrin cross-linking, said to becross-linked to such a degree that the viscosity is up to 100% of itsmaximum viscosity, all as discussed in Col. 5, lines 41-48 of U.S. Pat.No. 4,822,500.

In sharp contrast, the starch derivative according to the presentinvention is non-hydroxylpropylated and is formulated from highamylopectin (at or near 100% amylopectin content) waxy maize. The starchderivative of the present invention has only a moderate degree ofepichlorohydrin cross-linking, such that it reaches a viscosity of only40 to 60% of its maximum peak viscosity.

The starch used in the present invention is cross-linked withepichlorohydrin in a basic aqueous-starch suspension at a temperatureand for a period of time such that the Brabender viscosity of thesuspension is within about 30 to 70% of the maximum peak viscosity whichcan be obtained in the starch suspension, as determined experimentally,using a Brabender measurement. Preferably the starch is cross-linkedsuch that it reaches a viscosity of about 40 to 60% of the maximum peakviscosity. When the desired viscosity is reached, the cross-linkingreaction is terminated. A Brabender Viscometer is a standard viscometerreadily available on the open market and well known to those skilled inthe art.

The starch according to the present invention is cross-linked to amoderate level with 1-chloro 2,3-epoxypropane. The level or degree ofcross-linking is crucial to performance in terms of rheology, fluid lossand thermal stability within a given system.

The degree of cross-linking is dependent upon several tightly controlledprocessing variables, which include starch concentration given in termsof Buame', epichlorohydrin concentration, pH (dependent upon alkaliconcentration), agitation, temperature, pressure, and time. Each ofthese variables influence the rate of the cross-linking reaction, whichin turn determines the optimum degree of cross-link within a certainperiod of time.

It has been determined that the optimum range of cross-link for thestarch derivation according to the present invention is a moderate levelas measured by a standard Brabender Amylograph, with a viscosity equalto 30 to 70% of the maximum BBU peak viscosity at a 6% solids level.

Samples of the starch derivative according to the present invention weretested in the laboratory, in comparison with the low amylopectin starchproduct, as a filtration control agent in various well fluids. Thestarches were tested and screened in a 12.5 lb./gal. fluid because it ismore difficult to obtain filtration control while maintainingrheological properties in higher density (more solids) fluids. Thefluids were rolled at 150° F. for 16 hours before testing. Thefiltration tests were conducted on a 10 micron core at 250° F. with 500psi differential pressure.

Laboratory tests comparing similar concentrations of the highamylopectin and low amylopectin-derived starches indicate that the highamylopectin-derived starch is more efficient than the lowamylopectin-derived starch at filtration control in high densitysaturated salt solutions.

As is well known in the art, the filtration properties of drillingfluids, sometimes referred to as drilling muds, must be carefullycontrolled. In order to prevent formation fluids from entering theborehole, the hydrostatic pressure of the mud column must be greaterthan the pressure of the fluids in the pores of the formation.Consequently, mud tends to invade permeable formations. Massive loss ofmud into the formation usually does not occur, because the mud solidsare filtered out onto the walls of the hole, forming a cake ofrelatively low permeability, through which only filtrate can pass. Mudsmust be treated to keep cake permeability as low as possible in order tomaintain a stable borehole and to minimize filtration invasion of, anddamage to, potentially productive horizons. Furthermore, high cakepermeabilities result in thick filter cakes, which reduce the effectivediameter of the hole and cause various problems, such as excessivetorque when rotating the pipe, excessive drag when pulling it, and highswab and surge pressures. Thick cakes may cause the drill pipe to stickby a mechanism known as differential sticking, which may result in anexpensive fishing job.

Two types of filtration are involved in drilling an oil well; staticfiltration, which takes place when the mud is not being circulated, andthe filter cake grows undistributed, and dynamic filtration when the mudis being circulated and the growth of the filter cake is limited by theerosive action of the mud stream. Dynamic filtration rates are muchhigher than static rates, and most of the filtrate invading subsurfaceformations does so under dynamic conditions. The filtration propertiesof drilling fluids are usually evaluated and controlled by the APIfilter loss test, which is a static test, and is therefore not areliable guide to downhole filtration unless the differences betweenstatic and dynamic filtration are appreciated, and the test resultsinterpreted accordingly.

Static tests are sometimes conducted with paper, which are generally notreliable tests because oil and gas wells obviously are not drilledthrough paper. The laboratory tests which were conducted by theapplicant, while static, were done using a 10μ ceramic cylinder whichclosely approximates the sandstone formations which are commonly drilledthrough in the Gulf of Mexico, offshore Texas and Louisiana, and thusclosely simulates actual drilling conditions.

The results of applicant's static filtration test are identified in theaccompanying Tables 1-7, under the headings HTHP filtrate 250° F., 10 μmcore. The parameters related to filtration are spurt volume, measured inmL and total volume, measured in mL. Although the 10μ ceramic cylinderis more accurate than the paper test, it should be appreciated that theresults of such tests may differ up to 15 to 25% when repeated on thesame sample.

It should be appreciated that a small volume of fluid lost to theformations is good, in that the formation will be softened up tofacilitate the drilling of the formation. Consequently, it is notdesirable that either the total volume or the spurt volume of thefiltrate be zero. However, for comparative tests, the lower the numberthe better both for the total volume of the filtrate, as well as for thespurt volume of the filtrate.

The theory of filtration properties of drilling fluids is well known,and is described at length, for example, in Chapter 6, pages 277-312 ofthe above-identified book of George R. Gray et al., entitled Compositionand Properties of Oil Well Drilling Fluids, Fourth Edition, and need notbe described herein.

Referring now to the accompanying Table 1, there is a comparison offiltration control between the hydroxypropyl starch (low amylopectin)and the non-hydroxylpropyl starch (high amylopectin) in accord with thepresent invention. The data in Table 1 illustrates that use of the highamylopectin in a wide variety of drilling, completion and workoverfluids can reduce the rate of fluid loss, including high densitysaturated NaCl brine solutions (i.e., 10 lb/gal NaCl Brine) in thepresence of xanthan gum (i.e., N-VIS).

The ingredient shown as N-DRIL HT is a low amylopectin starch. Theingredient listed as N-VIS-P is comprised of one-fourth xanthan gum andthree-fourths low amylopectin starch. Thus, when determining theconcentration of low amylopectin in a fluid, one must add the lb/bbl ofN-DRIL HT to three-fourths the lbs/bbl of N-VIS-P. For example, inSample A of Table 1 the fluid contains 3 lb/bbl N-VIS-P and 8 lb/bblN-DRIL-HT, thus the actual amount of low amylopectin in the fluid wouldbe 10.25 lb/bbl (3×75=2.25; 8+2.25=10.25). In Tables 1 through 7 theconcentration of N-DRIL HT is set out and the total concentration of lowamylopectin given in parenthesis (i.e., N-DRIL HT plus 0.75×N-VIS-P).

Similarly, in comparing different concentrations of the biopolymerxanthan gum in the different fluids one would compare the lb/bbl ofN-VIS with one-fourth the lb/bbl of N-VIS P.

In the various Tables 1-7, when referring to the “10 lb/gal NaClBrine”,this indicates a saturated NaCl brine solution in which theaddition of sized salt particles will not dissolve because the brine isalready saturated. BARAPLUG 20, BARAPLUG 40 and BARAPLUG 50 are sizedsalt particles marketed by Baroid Drilling Fluids, Inc. of Houston,Tex., and which have mean particle sizes of 20, 40 and 50 micronsrespectively. Similarly, BARACARB 5 and BARACARB 50 are sized calciumcarbonate particles which have a mean particle size of 5 and 50 micronsrespectively.

Optimum drilling fluids must be able to limit filtration under a varietyof conditions. Tables 1 through 7 give the test results using a varietyof drilling fluids. Table 1 provides a good summary of the differenttypes of drilling fluid tested.

Sample A (containing 10.25 lb/bbl of low amylopectin starch and 0.75lb/bbl of xanthan gum in fresh water with calcium carbonate particles)had a spurt volume of 1.8 and a total volume of 18.2. Sample B(containing 8 lb/bbl of high amylopectin and 1.0 lb/bbl of xanthan gumin fresh water with calcium carbonate particles) had a spurt volume of2.0 and a total volume of 20.8. Thus, Samples A and B were similar intheir capacity to limit filtration in fresh water solutions havingcalcium carbonate particles suspended therein. However, Sample Acontained a 28% higher concentration of low amylopectin than theconcentration of high amylopectin in Sample B.

Sample C (containing 10.75 lb/bbl of low amylopectin starch and 0.25lb/bbl of xanthan gum in brine with calcium carbonate particles) had aspurt volume of 1.2 and a total volume of 17.2. Sample D (containing 8lb/bbl of high amylopectin and 0.25 lb/bbl of xanthan gum in brine withcalcium carbonate particles) had a spurt volume of 1.8 and a totalvolume of 16.2. Thus, Samples C and D were also similar in theircapacity to limit filtration, even though Sample C contained a 34%higher concentration of low amylopectin than the concentration of highamylopectin in Sample D.

Sample E (containing 11.5 lb/bbl of low amylopectin starch and 0.5lb/bbl of xanthan gum in saturated brine with suspended sodium chlorideparticles) had a spurt volume of 3.2 and a total volume of 22.2. SampleF (containing 10 lb/bbl of high amylopectin and 0.25 lb/bbl of xanthangum in saturated brine with suspended sodium chloride particles) had aspurt volume of 2.8 and a total volume of 18.8. Thus, Samples E and Fwere similar in their capacity to limit filtration in saturated saltsolutions, even though Sample E contained a 15% higher concentration oflow amylopectin than the concentration of high amylopectin in Sample Fand twice as much xanthan gum as Sample F.

Sample G (containing 8.75 lb/bbl of low amylopectin starch and 0.25lb/bbl of xanthan gum in saturated brine with a high density ofsuspended sodium chloride particles) had a spurt volume of 3.2 and atotal volume of 31.2. Sample H (containing 8 lb/bbl of high amylopectinand 0.25 lb/bbl of xanthan gum in saturated brine with a high density ofsuspended sodium chloride particles) had a spurt volume of 1.4 and atotal volume of 18.6. These results illustrate that the high amylopectinis more effective at filtration control than the low amylopectin and isparticularly effective in high density salt solutions.

The data in Table 2 illustrates that the use of xanthan gum incooperation with the high amylopectin in drilling and workover fluidscan further reduce the rate of fluid loss in fresh water solutions.

Table 2 compares fluids that contain the low and high amylopectin starchin combination with xanthan gum in fresh water. The results given inTable 2 illustrate that low concentrations of the high amylopectin (4-6lb/bbl) can be used in drilling, workover and completion fluids whileretaining the desired filtration control. However, increasedconcentrations of the xanthan gum are needed in these fluids to maintainthe appropriate viscosity and suspension properties of the fluids (i.e.,yield point). For example, at low concentrations of amylopectin starch(see Samples C-F of Table 2) the concentration of xanthan gum becomesvery important in the control of the yield point of the fluid. Samples Cand E both contain 4 lb/bbl of high amylopectin, with Sample C having1.25 lb/bbl of xanthan gum and Sample E having 0.75 lb/bbl of xanthangum. The yield point of Sample C was 24 lb/100 ft² and the yield pointof Sample E was 13 lb/100 ft². Desirable yield points drilling, workoverand completion fluids typically range from 18 to 40 lb/100 ft².Similarly, Samples D and F both contain 6 lb/bbl of high amylopectin,with Sample D having 1.25 lb/bbl of xanthan gum and Sample F having 0.75lb/bbl of xanthan gum. The yield point of Sample D was 25 lb/100 ft² andthe yield point of Sample F was 18 lb/100 ft². At the higherconcentrations of amylopectin starch (i.e., 8 lb/bbl), the yield pointwas less sensitive to the concentration of xanthan gum as seen in SampleH having a xanthan gum concentration of 0.75 lb/bbl and a yield point of20 lb/100 ft².

Table 3 illustrates the increased efficiency of the high amylopectinversus the low amylopectin in the presence of xanthan gum in saturatedbrine. For example, Sample A (containing 8.75 lb/bbl of low amylopectinand 0.25 lb/bbl of xanthan gum) is less efficient at controlling totalvolume loss than is either Sample B (containing 6 lb/bbl of highamylopectin and 0.25 lb/bbl of xanthan gum) or Sample C (containing 8lb/bbl of high amylopectin and 0.25 lb/bbl of xanthan gum). Sample Aexhibits a total volume of 32, while Sample B and C have total volumesof 22.2 and 16.2 respectively.

Table 4 compares three saturated salt fluids with suspended saltparticles containing low amylopectin at 7.5, 9.5 and 11.5 lb/bbl with avariety of fluids containing 6-10 lb/bbl of the high amylopectin. Thehigh amylopectin containing fluids were consistently as good or betterthan the fluids made with the low amylopectin at controlling fluid loss.

Table 5 compares different concentrations of high and low amylopectinsolutions containing 0.25 lb/bbl of xanthan gum in saturated saltsolutions having a high density of suspended sodium chloride particles.Samples A, B and C have 6.75, 8.75 and 10.75 lb/bbl of low amylopectinrespectively. One of the problems often encountered with high densityfluids is that they exhibit unacceptable Theological properties. Forexample, Sample C having 10.75 lb/bbl of low amylopectin exhibits ayield point of 59. Yield point is a measure of fluid viscosity and thesuspension properties of the fluid. Yield points over about 40 lb/ft²are unacceptable for a drilling or workover fluid to be used in thefield. Thus, in high density fluids it is an advantage to be able toreduce the concentration of amylopectin and thereby decrease the yieldpoint of the fluid while maintaining adequate filtration control.

The results of Table 5 demonstrate that the high amylopectin givesbetter filtration control at lower concentrations than the lowamylopectin in high density saturated salt solutions. For example,Sample A having 6.75 lb/bbl of low amylopectin gave a spurt volume of4.0 and a total volume of 84 as compared to the spurt volume of 3.0 andtotal volume of 34.6 given by Sample D having 4 lb/bbl of highamylopectin. Likewise, Samples E and G having 6 lb/bbl of highamylopectin gave at least as good filtration control as did Sample Bhaving 8.75 lb/bbl of low amylopectin.

Tables 1 through 5 provide data on various drilling, workover andcompletion fluids incorporating a preferred preparation of the highamylopectin. Tables 6 and 7 provide data on the characteristics of someof the different preparations of the low and high amylopectin.

In Table 6, Samples A, B and C are low amylopectin containing fluids inwhich the starch has been carboxymethylated. It is apparent from thespurt volume and total volume of these samples that carboxymethylationof the amylopectin reduces the filtration control properties of thesesamples. Sample D represents a low amylopectin preparation that was nothydroxypropylated like the N-DRIL HT. Sample D had a similar spurtvolume and total volume as the N-DRIL HT sample, but the yield point wassubstantially higher for the non-hydroxypropylated sample (i.e., 50lb/ft² versus 39 lb/ft²).

The second portion of Table 6 illustrates the effectiveness of highamylopectin samples with different levels of crosslinking in saturatedsalt solutions containing a high density of sodium chloride particles.Although all of the yield points of these solutions are too high to beof practical value in the field, the mean value of the total volumes ofthe lightly crosslinked (Samples F, H and J), the moderately crosslinked(Samples E, I and K) and the highly crosslinked (Sample G) highamylopectin samples were lower than the total volume of the lowamylopectin sample.

Table 7 compares similar samples to those investigated in Table 6 infresh water fluids. Samples L, M, N, C, O, and P all represent lowamylopectin preparations where the amylopectin and amylose have beencarboxymethylated. In fresh water these fluids have an acceptable yieldpoint and give reasonable filtrate control. Samples Q and R representhigh amylopectin containing solutions in fresh water. These two sampleshave acceptable yield points and reasonable filtrate control. Sample Qis lightly crosslinked and Sample R is moderately crosslinked. In freshwater the moderately crosslinked Sample R has a better yield point andfiltrate control than the lightly crosslinked Sample Q.

In summary, the test results shown in Tables 1-7 demonstrate that use ofthe high amylopectin drilling, completion and workover fluids can reducethe rate of fluid loss. The use of high amylopectin in saturated NaClbrine solutions having a high density of sodium chloride particles isparticularly important because of the difficulty encountered withcurrently available low amylopectin fluids in maintaining reasonablefiltration control and desirable rheological properties under thoseconditions. The data shown in Tables 1-7 conclusively demonstrate theimproved efficiency of the high amylopectin-derived starch, and theimproved combination of such starch with the xanthan gum in a saturatedsalt solution for use in drilling fluids for drilling, completion andwork-over of oil and gas wells.

TABLE 1 Sample # A B C D E F G H Fresh water, bbl 0.95 0.95 — — — — — —10 lb/gal NaCl Brine, bbl — — 0.8 0.8 0.94 0.94 0.69 0.69 N-VIS, lb — 1— 0.25 — 0.25 — 0.25 N-VIS P, lb 3 — 1 — 2 — 1 — N-DRIL HT (actual), lb8(10.25) — 10(10.75) — 10(11.5) — 8(5.75) — High Amylopectin, lb — 8 — 8— 10 — 8 BARACARB ® 5, LB 20 20 25 25 — — — — BARACARB 50, LB 25 25 164164 — — — — BARAPLUG ™ 20, lb — — — — 20 20 90 90 BARAPLUG 40, lb — — —— 16 16 76 76 BARAPLUG 50, lb — — — — 10 10 70 70 BARABLF ®, lb 0.1 0.13.0 3.0 3.0 3.0 3.0 3.0 Rolled @ 150° F., hr 16 16 16 16 16 16 16 16Stirred, min 15 15 15 15 15 15 15 15 Temperature, ° F. 120 120 120 120120 120 120 120 Mud weight, lb/gal 9.0 9.0 12.5 12.5 10.5 10.5 12.5 12.5Plastic viscosity, cP 13 11 41 26 25 23 57 56 Yield point, lb/100 ft² 2324 39 26 25 19 38 42 10 sec gel, lb/100 ft² 5 10 15 7 5 4 7 7 10 secgel, lb/100 ft² 7 12 17 9 6 6 9 9 pH 9.8 9.7 8.9 9.0 9.2 8.8 9.0 8.9HTHP filtrate @ 250° F., 10 μm core Spurt volume, mL 1.8 2.0 1.2 1.8 3.22.8 3.2 1.4 Total volume, mL 18.2 20.8 17.2 16.2 22.2 18.8 31.2 18.6FANN 35 Dial Readings 600 rpm 49 46 121 78 75 65 152 154 300 rpm 36 3580 52 50 42 95 98 200 rpm 30 30 64 40 40 32 73 75 100 rpm 22 24 26 29 2721 46 48 6 rpm 7 10 17 8 6 5 8 9 3 rpm 5 12 16 7 5 4 7 7

TABLE 2 Sample # A B C D E F G H I Fresh water, bbl 0.95 0.95 0.95 0.950.95 0.95 0.95 0.95 0.95 N-VIS, lb — — 1.25 1.25 0.75 0.75 1.0 0.75 1.0N-VIS P, lb 2 3 — — — — — — — N-DRIL HT (actual), lb 8(9.5) 8(10.25) — —— — — — — High Amylopectin, lb — — 4 6 4 6 8 9 10 BARACARB 5, lb 20 2020 20 20 20 20 20 20 BARACARB 50, lb 25 25 25 25 25 25 25 25 25 BARABUF,lb 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Rolled @ 150° F., hr 16 16 16 1616 16 16 16 16 Stirred, min 15 15 15 15 15 15 15 15 15 Temperature, ° F.120 120 120 120 120 120 120 120 120 Mud weight, lb/gal 9.0 9.0 9.0 9.09.0 9.0 9.0 9.0 9.0 Plastic viscosity, cP 11 13 8 10 6 8 11 15 16 Yieldpoint, lb/100 ft 11 23 24 25 13 18 24 20 32 10 sec gel, lb/100 ft² 2 511 10 5 6 10 7 11 10 sec gel, 1b/100 ft² 3 7 14 14 7 8 12 9 13 pH 9.69.8 9.7 9.6 9.8 9.8 9.7 9.6 9.7 HTHP filtrate @ 250° F., 10 μm coreSpurt volume, mL 2.0 1.8 1.8 1.8 4.2 3.0 2.0 2.0 1.8 Total volume, mL20.0 18.2 24.2 22.2 25.8 22.6 20.8 19.2 16.6 FANN 35 Dial Readings 600rpm 33 49 40 45 25 34 46 50 64 300 rpm 22 36 32 35 19 26 35 35 48 200rpm 17 30 28 30 15 20 30 30 42 100 rpm 12 22 24 25 11 17 24 24 32 6 rpm3 7 13 14 5 7 11 8 13 3 rpm 2 5 11 11 4 5 10 7 11

TABLE 3 Sample # A B C D E F 10 lb/gal NaCl Brine, bbl 0.80 0.80 0.800.80 0.80 0.80 N-VIS, lb — 0.25 0.25 0.5 0.5 — N-VIS P, lb 1 — — — — 1N-DRIL HT (actual), lb 8(8.75) — — — — 10(10.1) High Amylopectin, lb — 68 6 8 — BARACARB 5, lb 25 25 25 25 25 25 BARACARB 50, lb 164 164 164 164164 164 BARABUF, lb 3.0 3.0 3.0 3.0 3.0 3.0 Rolled @ 150° .F, hr 16 1616 16 16 16 Stirred, min 15 15 15 15 15 15 Temperature, ° F. 126 120 120120 120 120 Mud weight, lb/gal 12.5 12.5 12.5 12.5 12.5 12.5 Plasticviscosity, cP 30 20 26 28 40 41 Yield point, lb/100 ft² 29 20 26 28 4239 10 sec gel, lb/100 ft² 13 5 7 7 9 15 10 sec gel, lb/100 ft² 15 7 9 912 17 pH 9.1 9.2 9.0 8.9 9.0 8.9 HTHP filtrate @ 250° F., 10 μm coreSpurt volume, mL 2.0 1.5 1.8 2.0 1.8 1.2 Total volume, mL 32 22.2 16.222.0 14.2 17.2 FANN 35 Dial Readings 600 rpm 89 60 78 84 122 120 300 rpm59 40 52 56 82 80 200 rpm 48 30 40 44 66 64 100 rpm 35 21 29 31 47 46 6rpm 15 6 8 8 13 17 3 rpm 15 5 7 7 10 16

TABLE 4 Sample # A B C D E F G H I J 10 lb/gal NaCl Brine, bbl 0.94 0.940.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 N-VIS, lb — — — 0.50 0.50 0.750.75 0.75 0.50 0.25 N-VIS P, lb 2 2 2 — — — — — — — N-DRILHT(actual), lb6(7.5) 8(9.5) 10(11.5) — — — — — — — High Amylopectin, lb — — — 6 8 6 810 10 10 BARAPLUG 20, lb 20 20 20 20 20 20 20 20 20 20 BARAPLUG 40, lb16 16 16 16 16 16 16 16 16 16 BARAPLUG 50, LB 10 10 10 10 10 10 10 10 1010 BARABUF, lb 3 3 3 3 3 3 3 3 3 3 Rolled @ 150° F., hr 16 16 16 16 1616 16 16 16 16 Stirred, min 15 15 15 15 15 15 15 15 15 15 Temperature, °F. 120 120 120 120 120 120 120 120 120 120 Mud weight, lb/gal 10.5 10.510.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 Plastic viscosity, cP 14 19 2513 18 14 20 28 27 23 Yield point, lb/100 ft² 15 21 25 15 23 20 28 42 3619 10 sec gel, lb/100 ft² 3 3 5 4 5 5 7 10 7 4 10 sec gel,lb/100 ft² 5 56 6 7 7 10 12 9 6 pH 9.1 9.2 8.9 9.0 9.0 9.1 9.0 8.9 9.0 8.8 HTHPfiltrate @ 250° F., 10 μm core Spurt volume, mL 4.8 4.0 3.2 4.2 4.0 4.64.0 3.0 3.2 2.8 Total volume, mL 24.2 23.4 22.2 38.6 23.8 36.6 23.0 19.621.6 18.8 FANN 35 Dial Readings 600 rpm 43 59 75 41 59 48 68 98 90 65300 rpm 29 40 50 28 41 34 48 70 63 42 200 rpm 22 32 40 21 33 28 40 58 5032 100 rpm 16 22 27 15 23 20 29 42 36 21 6 rpm 4 5 6 5 6 7 9 12 9 5 3rpm 3 3 5 4 5 5 7 10 7 4

TABLE 5 Sample # A B C D E F G H 10 lb/gal NaCl Brine, bbl 0.69 0.690.69 0.69 0.69 0.69 0.69 0.69 N-VIS, lb — — — 0.25 0.25 0.25 0.25 0.25N-VIS P, lb 1 1 1 — — — — — N-DRIL HT (actual), lb 6(6.75) 8(8.75)10(10.75) — — — — — High Amylopectin, lb — — — 4 6 8 6 8 BARAPLUG 20, lb90 90 90 90 90 90 90 90 BARAPLUG 40, lb 76 76 76 76 76 76 76 76 BARAPLUG50, LB 70 70 70 70 70 70 70 70 BARABUF, lb 3.0 3.0 3.0 3.0 3.0 3.0 3.03.0 Rolled @ 150° F., hr 16 16 16 16 16 16 16 16 Stirred, min 15 15 1515 15 15 15 15 Temperature, ° F. 120 120 120 120 120 120 120 120 Mudweight, lb/gal 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 Plasticviscosity, cP 41 57 81 40 41 57 39 56 Yield point, lb/000 ft² 26 38 5920 26 47 25 42 10 sec gel, lb/100 ft² 5 7 12 6 6 6 5 7 10 sec gel,lb/100 ft² 6 9 13 7 8 8 7 9 pH 8.9 9.0 9.0 8.9 9.0 8.9 8.9 9.0 HTHPfiltrate @ 250° F., 10 μm core Spurt volume, mL 4 3.2 2.4 3.0 3.0 3.02.0 1.4 Total volume, mL 84 31.2 19.6 34.6 26.0 19.0 26.0 18.6 FANN 35Dial Readings 600 rpm 108 152 221 100 108 161 103 154 300 rpm 67 95 14060 67 104 64 98 200 rpm 50 73 108 46 51 80 49 75 100 rpm 33 46 70 30 3251 31 48 6 rpm 7 8 15 6 7 9 6 9 3 rpm 5 7 12 5 6 6 5 7

TABLE 6 Sample Sample Sample Sample Sample Sample Sample Sample SampleSample Sample Sample # N-DRIL HT A B C D F H J E I K G 10 lb/gal NaClBrine, bbl 0.69 0.69 0.69 0.69 0.69 0.69 0.69 0.69 0.69 0.69 0.69 0.69N-VIS, lb — 0.25 0.25 0.25 0.25 — 0.25 0.25 0.25 0.25 0.25 0.25 N-VIS P,lb 1 — — — — — — — — — — — N-DRIL HT (actual), lb 8(8.75) — — — — — — —— — — — Low Amylopectin, lb — 8.75 8.75 8.75 8.75 High Amylopectin, lb8.75 8.75 8.75 8.75 8.75 8.75 8.75 BARAPLUG 20, lb 90 90 90 90 90 90 9090 90 90 90 90 BARAPLUG 40, lb 76 76 76 76 76 76 76 76 76 76 76 76BARAPLUG 50, LB 70 70 70 70 70 70 70 70 70 70 70 70 BARABUF, lb 3.0 3.03.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Rolled @ 150° F., hr 16 16 16 1616 16 16 16 16 16 16 16 Stirred, min 15 15 15 15 15 15 15 15 15 15 15 15Temperature, ° F. 120 120 120 120 120 120 120 120 120 120 120 120 Mudweight, lb/gal 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.5 12.512.5 Plastic viscosity, cP 58 64 52 60 70 57 68 75 68 76 75 64 Yieldpoint, lb/100 ft² 39 48 40 37 50 40 46 65 57 74 66 50 10 sec gel, lb/100ft² 6 4 6 5 8 5 9 12 8 12 13 8 10 sec gel, 1b/100 ft² 8 7 8 7 10 7 11 1510 15 15 9 pH 8.9 9.0 9.0 9.0 8.9 9.0 9.1 8.9 9.0 9.0 9.0 9.1 HTHPfiltrate @ 250° F., 10 μm vore Spurt volume, mL 3.0 7.0 5.0 6.0 3.6 4.03.6 2.2 4.0 2.6 2.3 3.0 Total volume, mL 29.0 69.0 79.0 54.0 23.6 16.425.4 20.2 24.0 15.4 18.6 14.6 FANN 35 Dial Readings 600 rpm 155 176 144157 190 154 182 215 193 226 216 178 300 rpm 97 112 92 97 120 97 114 140125 150 141 114 200 rpm 74 82 77 73 92 74 90 110 97 120 111 87 100 rpm47 56 50 46 60 46 58 72 62 80 73 56 6 rpm 8 5 8 6 10 7 10 14 11 15 16 103 rpm 6 4 7 5 7 5 8 12 8 11 13 8

TABLE 7 Sample # N-DRIL HT Sample L Sample M Sample N Sample C Sample OSample P Fresh water, bbl 0.74 0.74 0.74 0.74 0.74 0.74 0.74 N-VISP, lb1 — — — — — — N-DRIL HT, lb 8(8.75) — — — — — 0.25 N-VIS, lb — 0.25 0.250.25 0.25 0.25 8.75 Low Amylopectin, lb — 8.75 8.75 8.75 8.75 8.75 25BARACARB 5, lb 25 25 25 25 25 25 212 BARACARB 50, lb 212 212 212 212 212212 0.1 BARABUF, lb 0.1 0.1 0.1 0.1 0.1 0.1 Rolled @ 150° F., hr 16 1616 16 16 16 16 Stirred, min 15 15 15 15 15 15 15 Temperature, ° F. 120120 120 120 120 120 120 Mud weight, lb/gal 12 12 12 12 12 12 12 Plasticviscosity, cP 23 27 40 33 31 30 42 Yield point, lb/100 ft² 20 14 36 1.814 25 28 10 sec gel, lb/100 ft² 5 2 12 4 3 4 4 10 sec gel, lb/100 ft² 73 14 6 4 6 6 pH 9.4 9.9 9.4 9.7 9.8 9.9 9.9 HTHP filtrate @ 250° F., 10μm core Spurt volume,mL 1.4 2.0 2.5 3.0 2.0 1.8 2.4 Total volume, mL30.2 14.0 16.8 15.2 16 14.4 16.6 FANN 35 Dial Readings 600 rpm 66 68 11684 76 85 112 300 rpm 43 41 76 51 45 55 70 200 rpm 34 31 57 40 34 40 52100 rpm 24 20 49 25 20 25 31 6 rpm 9 3 13 5 4 5 5 3 rpm 8 2 12 4 3 4 4Sample # Sample Q Sample R Sample J Sample K Fresh water, bbl 0.74 0.74— — 10 lb/gal NaCl brine, bbl — — 0.8 0.8 N-VIS, lb 0.25 0.25 0.25 0.25High Amylopectin, lb 8.75 8.75 8.75 8.75 BARACARB 5, lb 25 25 25 25BARACARB 50, lb 212 212 164 164 BARABUF, lb 0.1 0.1 0.1 0.1 Rolled @150° F., hr 16 16 16 16 Stirred, min 15 15 15 15 Temperature, ° F. 120120 120 120 Mud weight, lb/gal 12 12 12 12 Plastic viscosity, cP 27 1745 48 Yield point, lb/100 ft² 22 20 57 63 10 sec gel, lb/100 ft² 4 4 1616 10 sec gel, lb/100 ft² 6 6 19 19 pH 9.8 10.0 9.3 9.5 HTHP filtrate @250° F., 10 μm core Spurt volume, mL 2.0 2.0 — — Total volume, mL 18.011.6 — — FANN 35 Dial Readings 600 rpm 76 54 147 159 300 rpm 49 37 102111 200 rpm 38 30 83 90 100 rpm 25 21 59 65 6 rpm 5 5 19 22 3 rpm 4 4 1720

What is claimed:
 1. A process for reducing the filtration of a drillingor treatment fluid into a treatment region in a hydrocarbon-bearingformation below a surface penetrated by a well bore, while said fluid iscirculating in said wellbore, the process comprising: (a) preparing auniversal fluid including: a first component selected from the groupconsisting of fresh water, a non-saturated, aqueous saline solution anda saturated saline solution; a second component selected from the groupconsisting of sized calcium carbonate, water soluble particle salt, andcombinations thereof; xanthan gum; and a non-hydroxylated,epichlorohydrin cross-linked, high amylopectin waxy maize starch; (b)drilling a wellbore; and (c) circulating said fluid in said wellboreduring the drilling of said wellbore.
 2. The process of claim 1, whereinthe starch contributes to the filter cake along the sides of theborehole.
 3. The method of claim 1 wherein said starch is moderatelycrosslinked.
 4. A method for reducing loss of treatment fluid in asubterranean wellbore comprising adding to said fluid a compositioncomprising non-hydroxylpropylated, epichlorohydrin cross-linked, highamylopectin waxy maize starch.
 5. The method of claim 4 furthercomprising adding xanthan gum to said fluid.
 6. The method of claim 5wherein said starch is in a saturated salt solution added to said fluid.7. The method of claim 6 wherein said saturated salt solution comprisessized calcium carbonate, water soluble particulate salt, or combinationsthereof.
 8. The method of claim 4 further comprising circulating saidcomposition with said fluid in said wellbore and allowing saidcomposition to comprise a filter cake on at least a portion of saidwellbore wall.
 9. The method of claim 4 wherein said treatment fluid isused for drilling, completion, or workover of the well.
 10. The methodof claim 4 wherein said addition to said fluid does not result insubstantial change in the rheology properties of the fluid.
 11. Themethod of claim 4 wherein the crosslinking of said starch is moderate.12. A method for limiting or controlling filtration of wellbore fluidinto a subterranean, hydrocarbon bearing formation in which saidwellbore fluid is circulated in a wellbore penetrating said formation,the method comprising: (a) adding to said fluid a solution comprisingnon-hydroxylpropylated, epichlorohydrin cross-linked, high amylopectinwaxy maize starch; (b) circulating said fluid in the wellbore; and (c)allowing said fluid to form a filter cake comprising said starch on thewall of said wellbore.
 13. The method of claim 12 wherein said wellborefluid is a drilling fluid.
 14. The method of claim 12 wherein saidwellbore fluid is a workover fluid.
 15. The method of claim 12 whereinsaid wellbore fluid is a well completion fluid.
 16. The method of claim12 wherein said solution further comprises xanthan gum.
 17. The methodof claim 12 wherein said solution further comprises a saturated brinecomprising suspended water soluble salt particles.
 18. The method ofclaim 12 wherein said solution further comprises a saturated brinecomprising calcium carbonate particles.
 19. The method of claim 12wherein said solution further comprises fresh water or brine.
 20. Themethod of claim 12 wherein said fluid has high density.
 21. The methodclaim 12 wherein the crosslinking of said starch is moderate.